Diaphragm for electrolytic cells



MI w. KREJCI AND G. E. JOHNSON.

DAPHRAGM FOR ELECTROLYTIC CELLS.

APPLICATION FILED JAN.16. |920.

Patented Nov. 16, 1920.

Gaymard UNITED STATES PATENT FFICE.

MILO W. KREJ'I, OF CHICAGO, ILLINOIS, AND GUNNARD E. JOHNSON, 0F HAMMOND, INDIANA.

DIAPHRAGM FOR ELECTROLYTIC CEL-LS.

Application filed January 16, 1920.

To @ZZ lwhom z' may concern.'

Be it known that we, MILo W. KREJI and GUNNARD E. JOHNSON, citizens of the United States, residing, respectively, at Chicago, county of Cook, State of Illinois, and at Hammond, county of Lake, State of Indiana, have invented certain new and useful Improvements in Diaphragms for Electrolytic Cells, of which the following is a full, clear, and exact description, reference being had to the accompanying drawings, forming a part hereof.

Our invention has relation to improvements in diaphragms for electrolytic cells, the same being applicable to any electrolyte be the same organic or inorganic, acid, neutral, or alkaline, one-fluid or bifluid, and whether employed for oxidizing or for reducing purposesl The diaphragm is eminently adapted for use in cells employed in the precipitation of metals and metallic compounds, an example of which may be seen in U. S. Patent No. 1,308,948, dated July 8, 1919, issued to R. M. Harrington, method of producing lead salts, and which we have herein selected in order to emphasize some of the numerous advantages inherent in and which flow from the use of our improved diaphragm. The object of the invention is to provide a diaphragm which shall be rigid and durable, one not affected by drying out, one resisting seepage, one which is inexpensive and not subject to frequent renewals, one having a maximum adsorbing power for the ions released by the current by reason of the increased surface of contact which the diaphragm presents to the ions during their passage therethrough in their travel from one electrode to the other; one which is long-lived and not readily disintegrable from constant use, one requiring practically no attention while in service, and one possessing further and other advantages better apparent from the following detailed description in connection with the accompanying drawings in which- Figure 1 represents a diagrammatic elevation of a bifluid cell for precipitating white lead showing our invention applied thereto; Fig. 2 is a perspective 'of the sheet or board forming the diaphragm; and Fig. 3 is an enlarged cross-section of the diaphragm.

Specification of Letters Patent.

Patented Nov. 16, 1920.

serieu No. 351,903.

Referring to the drawings, 1 represents a suitable cell or tank provided with a bottom hopper portion 2, from the discharge end of which leads a circulating pipe 3 to a settling tank 4, a pump 5 being disposed at a convenient point along the pipe. The settling tank is provided with a bottom discharge controlled by a valve or cock 6 for the discharge of the white lead which settles in the tank.l The clear liquid or anolyte is in turn discharged into the anolyte com'- partment A of the tank through the overflow pipe 7. The catholyte compartment C of the cell is formed by a wooden box or frame 8 immersed in the tank 1, the wall of the box facing or adjacent to the lead anode L in the anolyte being formed of an osmotic diaphragm 9 which permits of the necessary diffusion therethrough of the catholyte from the compartment C to the anolyte compartment A, and of the necessary traverse or passage of the ions from one electrode to the other, the cathode electrode E being preferably a sheet of iron. Leading from the bottom of the catholyte compartment is a circulating pipe 10 the opposite end of the pipe terminating in the bottom of the coke tower 11, from the upper portion of which leads a circulating pipe 12 to the catholyte compartment. A circulating pump 13 is disposed at a convenient point along the pipe 10, the latter being provided with a regulating valve 14 above the pump, and being connected to the pipe 12 by a shunt 15 at a point between the pump and said coke tower. This shunt is likewise provided with a regulating valve 16. The lower end of the coke tower is connected by a circulating pipe 17 to the upper end of a scrubber 18 to which the Hue gas containing carbon dioxid is conducted from any suitable source by the pipe 19. The apparatus herein described isv substantially that shown in the Harrington patent aforesaid and it will therefore be unnecessary to enlarge on the description. The anolyte when initiall charged into the anolyte compartment is an aqueous solution of sodium acetate, to which a small amount of sodium carbonate has been added, the catholyte containing substantially the same salts but with an alkalinity at least fifty times stronger than the anolyte as fully pointed out in the Harrington patent aforesaid, the alkali car bonate furnishing the necessary C()3 ions to combine with the incipient solution of lead acetate which forms at the anode, to proi luce a precipitate of basic lead carbonate (f2PbCO3Pb(OH)2) which as it settles in the hopper 2, is pumped into the settler 4 whence it is withdrawn through the valve or cock 6, and then filtered, washed, dried, pulverized and packed in barrels for the market. As previously pointed out, the diaphragm is osmotic, and not only allows' for the free passage therethrough of the ions released by the electric current but perm1ts of the necessary diffusion of the l1qu1ds therethrough by osmosis. It is this twofold action of the diaphragm which permits of a suiiicient number of CO3 ions and of a suicient amount of alkali carbonate to pass from the catholyte to the anolyte and there react with the lead acetateto form the basic carbonate of lead, the character of our diaphragm being such as to cause the rate of flow ofthe carbonate reagents (through it) from the catholyte to the anolyte to be commensurate with the rate of formation of the lead acetate in the anolyte.

It was intimated above that there must be no seepage through the diaphragm, that is to say, the diaphragm must not allow the electrolyte to pass through it at a greater 'rate than is determined by the necessary rate of diffusion of the electrolyte and the passage of the ions therethrough in proper direction to effect the desired chemical reactions for any given process: For example, in the precipitation of White lead, if undue quantities of sodiumcarbonate from the catholyte Were to find their way into the anolyte through the diaphragm by reason of seepage, or on account of a puncture in the diaphragm, the White lead would precipitate in the anolyte so rapidly as to form a coating on the lead anode, this coating being subsequently peroxidized by the oxygen released at the anode into lead oxid, which oxid would not only discolor the White lead but would in time arrest the action of the current, the oxid being a non-conductorA of electricity. Again, suppose that the diaphragm were so impervious to diffusion and its adsorbing power for the ions so low as to prevent or unduly retard the passage of the catholyte and the CO3 ions therethrough into the anolyte to effect at the proper time the desired chemical reaction, and that the sodium carbonate originally introduced into the anolyte was depleted (by reason of previous reactions), the resultwould be that the lead acetate formed at the anode, having no carbonio acid to react with it to precipitate the White lead, would under the action of the electric current drop its lead ion, thereby permitting lead to be deposited in sponge form at the cathode. This sponge,

dropping 'to the bottom of the catholyte compartment C would soon short-circuit with the diaphragm, and were the latter made of canvas or organic material, the current would shortly char and puncture the same, allowing undue leakage or seepage of the catholyte therethrough into the anolyte compartment, thereby giving rise to the first objections recited herein. Bythe use of our diaphragm no such consequences are possible or likely for the reason that the diaphragm permits of only the necessary rate of diffusion of the electrolyte and the passage of the ions therethrough, and being of mineral composition can not corrode 'even Were sponge lead for some unaccountable reason ever deposited at the cathode (which has never been the case).

In the example above, the diaphragm is shown applied to a bifluid cell, but it may be used in cells employing a one-fluid electrolyte. For example, in leaching copper ores with sulfuric acid, the resulting solution contains -not only sulfate of copper, but sulfates of iron and other metals. The iron which is in the ferrie state is first reduced to the' ferrous state by SO2 gases because in the electrolytic deposition of copper the ferric salt attacks the copper about to be deposited and dissolves the same, and no copper will deposit until the ferric salt is reduced at the cathode. Where the ferrie salt is rst reduced. to the ferrous form outside the cell or before the current is applied,

then when the current is passed through the electrolyte in the presence of our diaphragm, the ions of oxygen will peroxidize the ferrous salt on the side of the diaphragm facing the anode; and although the ferrie sulfate thus formed will in a measure diffuse slightly through the diaphragm into the catholyte compartment, it will again be harm to the precipitated copper. There is no occasion to further multiply the exam- Aples of the uses to which the diaphragm may be put, thesame being applicable for use in any electrolytic cell employing Huid or liquid electrolytes.

A diaphragm for electrolytic cells satisfactorily discharging the various functions imposed thereon by the conditions developed Within the cell has always been the great desz'deratum. Such a diaphragm we believe has been attained by our improve'.- ment. In the present embodiment of4 our invention the base or body of the diaphragm is min-eral wool (slag wool) which as well understood in the art is made by subjecting furnace slag while molten to a strong blast, the slag being reduced to fine loose threads or filaments which become more or less interlaced and resemble wool. It is essentially a silicate, and is sometimes referred to as silicate cotton. A similar substance also a silicate, made from lime and siliceous rocks melted together, is called rock wool. To the wool there is added just enough paraffin oil to form a suitable binder after which the same is pressed into sheet form with sufficient force to impart thereto a stiff boardlike consistence. We do not wish to be limited to paraffin oil as a binder, and any other suitable material not affected by the electrolyte might be used in lieu thereof. The paraffin oil however answers the purpose admirably, being proof against attack by alkaline, neutral, and acid electrolytes. In the present embodiment of our invention the base of the diaphragm, as above indicated, is an artificial vitrified filamentary compound or silicate, such as mineral wool, rock wool, wool glass, and the like. We do not wish to be understood however as limiting ourselves to the use of silicates, it being within the scope of our invention to employ flamentary substances that are not necessarily silicates. For example, it might be possible to use aluminates of lime, magnesia and the like in the form of filaments or fiber; and while a suitable binding material is desirable and perhaps essential, its omission would not constitute a departure from the basic principle of our invention which contemplates primarily, the use of a base of artificial filamentary or fibrous material preferably (though not necessarily) of mineral origin, and one capable of resisting attack or disintegration by the electrolyte be the latter acid, neutral, or alkaline. So far as we are aware no natural product seems to possess the necessary filamentary or interlaced fibrous or thread like structure as does mineral wool or artificially prepared mineral silicates (or their equivalents) to form an ideal diaphragm.' But should a natural product be discovered that possesses the necessary filamentary character, or to which such character may be imparted by artificial means, that also would fall within the scope of our invention; and in this connection we desire it to be understood that the filaments of our base may be of organic as well as of inorganic or mineral origin. The final product may be compared to a board of papier-mch, and in outward appearance is not unlike a sheet of commercial asbestos cloth except that it is of interlaced filamentary teXture and comparatively stiff (like a pine board). It makes an ideal osmotic diaphragm, possessing a maximum efficiency by reason of the high degree of ionization developed in the electrolyte by its use. It retains its shape under all conditions, not warping or bulging under osmotic pressure. A diaphragm two feet square would have a thickness between say one-quarter and three eighths of an inch. The degree of compression to which the wool filaments are subjected will depend on the osmotic or diffusion porosity desired, this depending more or less on the electrolyte in which the diaphragm is to be used. The object sought of course is to provide a diaphragm which permits of the maximum degree of ionization to take place in the electrolyte, this degree depending on the area of the surface presented t the ions traversing the diaphragm. The manner of incorporating the binder with the mineral wool is immaterial. The wool may be dipped into a bath of hot paraffin oil, then allowed to drain and finally subjected to pressure to form the finished board or diaphragm. In the pressing operation the excess of oil is squeezed out. Again, the hot paraffin oil might be sprayed on the wool until a sufficient quantity for binding purposes has been' absorbed after which the whole is subjected to pressure. Other meth ods might be resorted to for incorporating the binder without involving a departure from our invention.

Having described our invention what we claim is:

l. A diaphragm for electrolytic cells having a base composed of loose filaments of vitrified material compressed to operate osmotically. y

2. A diaphragm for electrolytic cells comprising a base of vitrifled mineral filaments in combination with a suitable binder, the whole being compressed to form an osmotic sheet.

3. A diaphragm for electrolytic cells comprising a base of mineral wool, in combination with a suitable binder, the whole being compressed into a porous body operating osmotically.

4. A diaphragm for electrolytic cells comprising a base of mineral wool, in combination with a binder of paraffin oil, the whole being pressed into an osmotic sheet or board.

5. A diaphragm for electrolytic cells having a base composed of artificial loose silicate filaments compacted into an osmotic sheet or board.

6. A diaphragm for electrolytic cells having a base composed of artificial, mineral filaments compressed into an osmotic sheet.

7. A diaphragm for electrolytic cells comprising a mass of interlaced filaments of mineral wool impregnated with paraffin oil as a binder, and pressed into the form of an osmotic sheet or board.

8. A diaphragm for electrolytic cells comprisng a body of artificially vitrifed material, in combination With a suitable binder and operating by osmosis.

9. A diaphragm for electrolytic cells comprising a body of artificially Vitrified material in flamentary form, in combination with a suitable binder, the Whole compressed into an osmotic sheet or board.

In testimony whereof We aix our signa- 10 tures at Chicago, county of Cook, State of Illinois, this 10th day of January, 1920.

. MILO W. KREJI.

GUNNARD E. JOHNSON. 

